1. Technical Field
This application relates to a twist drill for drilling with a countersink cutting arrangement, and a cutting tool with a countersink cutting arrangement, and a cutting-chamfering tool.
2. Background Information
This application relates to a drill for a drilling/chamfering tool as well as to a drilling/chamfering tool, i.e. a combination tool for metal-cutting machining of material, which is suitable for both drilling and chamfering. A drilling/chamfering tool is known, for example, from Federal Republic of Germany Patent Publication No. 92 06 148 U1.
A drilling/chamfering tool is usually composed of a base body or clamping ring carrying a cutting insert, such as an indexable insert, as chamfering tool and a drill clamped in the base body or clamping ring, the cutting insert being fastened on the base body or clamping ring in such a way that the cutting edge provided for generating a chamfer partly engages into a chip space of the twist drill. It is, therefore, not possible to clamp the drill in the base body or clamping ring in any desired is position. When adjusting the drilling depth, as far as possible, one has to make sure that the correct angular relation between the drill and the cutting insert for the chamfering operation is re-established.
Instead of fixing the chamfering insert with partial engagement in a chip flute of the drill, it is also possible, as known, for example, from International Patent Publication No. WO 94/25210, to fasten the chamfering insert on the base body or clamping ring in such a way that it is pressed against a groove bearing flank of the drill. In the tool known from International Patent Publication No. WO 94/25210, the chamfering insert is adjustable at right angles to the drill axis, so that the tool can be suitable for different drill diameters. When the drill is adjusted in longitudinal direction, the angle between drill and base body or clamping ring must in this tool also be adjusted anew.
International Patent Publication No. EP 0 519 233 A1 describes a drilling tool on whose outer periphery dovetail guides are formed on which an additional cutting member can be fastened and shifted in longitudinal direction. Furthermore, International Patent Publication No. EP 068 499 A1 describes a drilling/chamfering tool in which a drill with helical chip flutes can be inserted into an adaptor of the drilling/chamfering tool in such a way that it is shiftable in longitudinal direction. The longitudinal shift requires in this case a rotational movement of the drill, as the latter includes in the area of its shank a helical cutting face or guide face. The lead of the cutting face corresponds to the lead of the chip flutes, so that it is guaranteed that in case of a longitudinal adjustment, one chamfering insert will always abut the outer periphery of the drill in an area between the chip flutes.
Another problem of drilling/chamfering tools is the supply of cooling lubricant to the drill: cooling lubricant which is supplied through a central hole to the base body or clamping ring flows from the latter into the chip flutes of the drill. A purposeful supply of cooling lubricant to the cutting edges of the drill, which is necessary with minimum-quantity lubrication, is in this way at best possible to a limited extent only. Until now, drilling/chamfering tools according to the state of the art have been designed without coolant channels inside the drilling tool, which would enable a more purposeful supply of small quantities of cooling lubricant to the drill tip, because such channels would reduce the cross-section and thus the load-bearing capacity of the drill. The limited cooling and lubricating possibilities, on the other hand, lead to the fact that drilling/chamfering tools according to the state of the art are mainly used for smaller, maximally for medium drilling depths up to approximately three times the drill diameter.